Socially and professionally, most people rely upon video displays in one form or another for at least a portion of their work and/or recreation. Cathode ray tubes (CRTs) larger and heavier than comparable displays composed of liquid crystal devices (LCDs) or light-emitting diodes (LEDs), which can provide a visual image of comparable resolution without the traditional bulk and weight associated with CRTs.
More specifically, as they typically do not include a tube, an LCD or LED display may be quite thin and light weight, improving portability of laptop computers, video displays in vehicles and airplanes, and information displays that are mounted or set in eye catching locations.
A typical CRT display also requires more power to operate then does a comparably sized LED display. For example a 14″ CRT display may require 110 watts of power, whereas a 14″ LED display may require 30˜40 watts or less. This difference in power consumption may be significant in the field of portable devices that must operate from a battery. In addition, power conservation and low profile aspects are increasingly in demand for home and office products, where the savings in energy may total several hundred dollars per year.
A CRT operates by a scanning electron beam used to excite phosphorous-based materials on the back side of the screen. The intensity of each pixel may be associated with the intensity of the electron beam. With an LCD display, each pixel is a transient light emitting device that may be selectively adjusted to permit light to shine through the pixel.
Generally speaking, to create an LCD 100, as shown in FIG. 1, a first and second polarized glass plate 101, 103 are provided, each having microscopic grooves in the surface opposite from, but in line with, a polarizing film 105, 107. The first and second polarized glass plates 101, 103 are parallel to one another with the respective polarizing film of each transverse to the other. For illustrative purposes, the polarizing film 105 and grooves of first glass plate 101 run parallel to the page, such that they are represented as solid line. In contrast, the polarizing film 107 and grooves of second glass plate 103 are perpendicular to the page, such that they are represented as parallel cross sections.
Nematic liquid crystals 109 are then added between the first and second glass plates 101, 103. The grooves will cause the layer of molecules of liquid crystals 109 that are in contact with the grooved glass plates 101, 103 to align with the grooves. As the grooves of one glass plate 101 are transverse to the grooves of the other glass plate 103, the Nematic liquid crystal 109 will twist. In the 2-D illustration of FIG. 1 this twisting is represented as nematic liquid crystal 109 appearing to change in size as it progresses from glass plate 101 to glass plate 103.
As light 111 provided by light source 113 strikes first glass plate 101, it is polarized. The molecules in each layer of nematic liquid crystal 109 then guide the light 111 from layer to layer within nematic liquid crystal 109, and in so doing, twist the light 111 to align with the grooves and the polarized filter of the second glass plate 103.
If an electric charge is applied across nematic liquid crystal 109, the molecules of nematic liquid crystal 109 will untwist. As nematic liquid crystal 109 straightens out, the angle of the light 111 passing through from first glass plate 101 to second glass plate 103 also changes, and the cross polarization orientation between the first and second polarized plates 105, 107 blocks the passage of light 111. In an alternative configuration, glass plate 103 may be optionally replaced with a reflective surface, such as a mirror 115, or a mirrored surface. When the nematic liquid crystal 109 is properly aligned by a field, light 111 will enter the first glass plate 101 and be reflected off mirror 115 and back out through first glass plate 101. By changing the applied field and thus the twist in nematic liquid crystal 109, the amount of light reflected may be reduced and/or blocked entirely.
By varying the degree of twisting, the LCD 100 utilizing nematic liquid crystal 109 can control how much of light 111 passes through, thus providing a gray scale. When the external light 111 is colored, or the light 111 passes through a color filter before or after passing through the LCD 100, color images of varying intensity may also be provided.
Generally speaking, the cost of manufacturing an LCD display rapidly increases as the area of the display is increased. Nevertheless, consumer demand emphasizes ever-increasing display size and resolution. Typical manufacturing processes employed to provide the LCD components include photolithographic techniques and other semiconductor fabrication techniques suited to the fabrication of small-scale components established on wafer substrates, which may be only a few centimeters in diameter. Even with such small substrates, it is not uncommon to move, align and repeat the masking/structure defining process.
As a common LCD display for a laptop computer may have approximately a 12″ viewing area and a large screen display may be multiple times larger, the re-alignment tolerances of photolithographic processes permit the introduction of defects that may render the entire display unusable. As such, quality control measures discard a high percentage of displays before they are fully assembled. As such, displays, especially large displays, are generally more expensive than they might be if not for the manufacturer's need to recoup the costs for resources, time, precision tooling, and device failure rate.
Hence, there is a need for a process to provide a low cost active matrix display that overcomes one or more of the drawbacks identified above. The present invention satisfies one or more of these needs.